Demi-Lee, an Australian, received the transplant after contracting a virus that attacked her liver.

Normally, a patient receiving a transplant has to take immuno-suppressant drugs to stop the body’s defenses rejecting the foreign organ. That medication leaves the patient vulnerable to infections and disease.

But Demi-Lee has escaped that fate. Speaking to the Sydney Morning Herald, her physician, Dr. Alexander, explained why: "Normally the body's own immune system rejects any cells that are transplanted … but for some reason the cells that came from the donor's liver seemed to survive better than Demi-Lee's own cells.”

No patient has ever been known to change blood type in this way.

Dr. Alexander went on to say that Demi-Lee’s transformation “has huge implications for the future of organ transplants."

Nine months after 15-year-old Demi-Lee Brennan received a liver transplant, her health worsened. When her blood was tested, her blood type was found to have changed from O-negative to O-positive. Doctors realized that it was her own old blood cells that were making her ill. When her immuno-suppressant treatment was stopped, Demi-Lee recovered her health.

The Lucile Packard Children's Hospital at Stanford explains that the liver is located in the upper-right hand area of the abdomen and is responsible for more than 500 vital functions. Some of these functions include the following: the production of bile, which helps carry away waste and break down fats in the small intestine during digestion; the processing of hemoglobin; the conversion of excess glucose into glycogen for storage; and the production of cholesterol and special proteins to help carry fats through the body.